The Nonsymmetric Kaluza-Klein (Jordan-Thiry) Theory leads to a model of a modified acceleration that can fit an anomalous acceleration experienced by the Pioneer 10 and 11 spacecraft. The future positions of those spacecrafts are predicted using distorted hyperbolic orbit. A connection between an anomalous acceleration and a Hubble constant is solved in the theory together with a relation to a cosmological constant in CDMΛ model.In the paper we consider an exact solution of a point mass motion in the Solar System under an influence of an anomalous acceleration. We find two types of orbits: periodic and chaotic. Both orbits are bounded. This means there is no possibility to escape from the Solar System. Some possibilities to avoid this conclusion are considered. We resolve also a coincidence between an anomalous acceleration and the cosmological constant using a paradigm of modern cosmology. Relativistic effects and a cosmological drifting of a gravitational constant are considered. The model of an anomalous acceleration does not cause any contradiction with Solar System observations. We give a full statistical analysis of the model. We consider also a full formalism of the Nonsymmetric Jordan-Thiry Theory for the problem and present a relativistic model of an anomalous acceleration. We consider the model for General Relativity approximation, i.e. g µν = η µν (g µν = g νµ ).In this model there are no contradictions with General Relativity tests in the Solar System. Pioneer 10/11 spacecrafts will come back in 10 6 years (a time scale of our periodic solutions is 10 6 years). Moreover, almost relativistic or relativistic spacecrafts can escape from the Solar System. We consider also a model of a relativistic acceleration which is more complicated, with g µν = g νµ taken into account.